Pain is a perception mediated by the activation of certain brain structures. Pain is usually initiated when specialized neurons, termed nociceptors, which innervate the skin or other peripheral tissue, are activated by mechanical, thermal, chemical or other noxious stimuli. Pain is also experienced when peripheral or central neuronal structures involved in the processing of pain become hyperactive, e.g. as a result of trauma, ischemia or inflammation. Other causes of pain include disease-specific processes, metabolic disturbances, muscle spasm, and the onset of a neuropathic event or syndrome.
Pain treatment of almost any type usually includes one or more analgesic drugs which are usually classified into three groups: primary non-opioid, opioid, and co-analgesics, also known as adjuvants. Non-opioid analgesic drugs include acetaminophen and non-steroidal anti-inflammatory drugs or NSAIDs. These drugs can be effective for treating mild to moderate pain, but may have significant side-effects such as liver damage in the case of acetaminophen and gastric ulcers in the case of NSAIDs. Opioid drugs, sometimes referred to as “narcotics”, include natural substances such as opium, opium-derived substances, such as morphine, and semi-synthetic and synthetic substances, such as fentanyl. Co-analgesic medications are drugs that typically address indications other than pain relief, but possess analgesic action for certain painful conditions. An example of a co-analgesic drug is gabapentin, which has a primary indication for the treatment of epilepsy, but also is effective in treating some kinds of neuropathic pain.
Opioid drugs are commonly used to relieve moderate to severe pain. However, their usefulness is limited by tolerance and dependence that normally develop with chronic treatment. Opioid drugs such as morphine can be addictive and are associated with significant and potentially fatal side effects such as respiratory depression in addition to sedation and mental alteration, constipation, nausea, exaggerated pain sensitivity, hormonal disturbances, and alteration of the immune system.
Despite a wide range of available medical treatments, pain continues to afflict millions of individuals in the US alone and remains a profound burden to patients, health care, and business. New methods are required for increasing the efficacy of intervention and reducing the side effects associated with pain management in the clinical setting.